Earphones may be largely divided into open-type earphones and canal-type earphones.
Since the open-type earphones have a structure leaking a large amount of low-pitched sounds, the canal-type earphones are used much recently. The canal-type earphones have a structure of being inserted into the ear canals, have an excellent sensation of wearing, and can minimize leaking of low-pitched sounds as they are tightly attached to the ear canals.
Therefore, the canal-type earphones tend to be manufactured considering the shape of ear canals.
However, since the size and shape of ear canals vary from person to person, there is a problem in that it is practically difficult for an individual user to choose canal-type earphones fitted the user perfectly.
Meanwhile, a user may experience that low-pitched sounds are enhanced when general earphones including the canal-type earphones are pressed into the ears (inner ears). That is, it is known that strength of reproducing the low-pitched sounds is changed according to a degree of tightly attaching the earphones to the ears.
Like this, when attachment of the earphones to the ear canals is not solid, it is difficult to expect reproduction of high-quality sounds. Moreover, there is a tendency of turning the volume up to compensate for the leaking sound. This may be harmful to the ears. That is, it may lead to noise deafness. In addition, since external noises may leak into when attachment of the earphones to the ear canals is not solid, there is a tendency of turning the volume up to properly hear the sounds outputted from the earphones. That is, a user may also turn the volume up when the external noises are loud.
In addition, the external noises act as an obstacle in reproducing high-quality sounds. Although a technique of measuring external noises has been proposed before, there is a problem in that it is difficult to distinguish external noises from the voices of a human being since a microphone which measures the external noises receives the voices of a human being together with the external noises. Like this, there is a limit in improving sound quality due to the difficulties in measuring the external noises.
Since it is difficult to treat or recover auditory cells once they are damaged, a measure for determining whether the earphones are properly worn on (tightly attached to) the ears is needed to reproduce high-quality sounds at a proper sound volume. In addition, there also needs a measure for improving sound quality through correct measurement of external noise when a user makes a phone call or listens to music.